Protein kinases are a family of enzymes that catalyse the phosphorylation of specific residues in proteins. In general protein kinases fall into three groups; those which preferentially phosphorylate serine and/or threonine residues, those which preferentially phosphorylate tyrosine residues, and those which phosphorylate both tyrosine and Ser/Thr residues. Protein kinases are therefore key elements in signal transduction pathways responsible for transducing extracellular signals, including the action of cytokines on their receptors, to the nuclei, triggering various biological events. The many roles of protein kinases in normal cell physiology include cell cycle control including proliferation and cell growth, differentiation, metabolism, apoptosis, cell mobility, mitogenesis, transcription, translation and other signalling processes.
The Protein Tyrosine Kinase family (PTKs) can be divided into the cytoplasmic PTKs (CTKs) and the receptor PTKs (RTKs). The cytoplasmic PTKs include the SRC family, (including: BLK; FGR; FYN; HCK; LCK; LYN; SRC; YES and YRK); the BRK Family (including: BRK; FRK (PTK5), SAD; and SRM); the CSK family (including: CSK and CTK); the TEC family, (including BTK; ITK; TEC; MKK2 and TXK), the Janus kinase family, (including: JAK1, JAK2, JAK3 and Tyk2), the FAK family (including, FAK and PYK2); the Fes family (including FES and FER), the ZAP70 family (including ZAP70 and SYK); the ACK family (including ACK1 and ACK2); and the Abl family (including ABL and ARG). The RTK family includes the EGF-Receptor family (including, EGFR, HER2, HER3 and HER4); the Insulin Receptor family (including INS-R and IGF1-R); the PDGF-Receptor family (also known as the Class III receptors, including PDGFRα, PDGFRβ, CSF-1R, KIT, FLT3); the VEGF-Receptor family (including FLT1, FDR and FLT4); the FGF-Receptor family (including FGFR1, FGFR2, FGFR3 and FGFR4); the CCK4 family (including CCK4); the MET family (including MET and RON); the TRK family (including TRKA, TRKB, and TRKC); the AXL family (including AXL, MER, and SKY); the TIE/TEK family (including TIE and TIE2/TEK); the EPH family (including EPHA1, EPHA2, EPHA3, EPHA4, EPHA5, EPHA6, EPHA7, EPHA8, EPHB1, EPHB2, EPHB3, EPHB4, EPHB5, EPHB6); the RYK family (including RYK); the MCK family (including MCK and TYRO10); the ROS family (including ROS); the RET family (including RET); the LTK family (including LTK and ALK); the ROR family (including ROR1 and ROR2); The Musk family (including Musk); the LMR family (including LMR1, LMR2 and LMR3); and the SuRTK106 family (including SuRTK106). Similarly, the serine/threonine specific kinases comprise a number of distinct sub-families, including the extracellular signal regulated kinases, (p42/ERK2 and p44/ERK1); c-Jun NH2-terminal kinase (JNK); cAMP-responsive element-binding protein kinases (CREBK); the cyclin dependent kinases (CDKs); cAMP-dependent kinase (CAPK); mitogen-activated protein kinase-activated protein kinase (MAPK and its relatives); stress-activated protein kinase p38/SAPK2; mitogen- and stress-activated kinase (MSK); and protein kinases, PKA, PKB and PKC inter alia.
Additionally, the genomes of a number of pathogenic organisms possess genes encoding protein kinases. For example, the malarial parasite Plasmodium falciparum and viruses such as HPV and Hepatitis viruses appear to bear kinase related genes, suggesting that inhibition of kinases may be a useful therapeutic option in the diseases caused by these organisms.
Inappropriately high protein kinase activity has been implicated in many diseases resulting from abnormal cellular function. This might arise either directly or indirectly, for example by failure of the proper control mechanisms for the kinase, related for example to mutation, over-expression or inappropriate activation of the enzyme; or by over- or under-production of cytokines or growth factors also participating in the transduction of signals upstream or downstream of the kinase. In all of these instances, selective inhibition of the action of the kinase might be expected to have a beneficial effect. Diseases where aberrant kinase activity has been implicated include immunological and inflammatory diseases such as Atopic Dermatitis, asthma, rheumatoid arthritis, Crohn's disease, psoriasis, inflammatory bowel disease, multiple sclerosis, Alzheimers disease and Type I diabetes; hyperproliferative diseases such as cancer for example prostate cancer, colon cancer, gastrointestinal tumors, breast cancer, head and neck cancer, leukemia including acute myelogenous leukemia (AML) and chronic myelogenous leukemia (CML) and lymphoma and diseases involving neo-angiogenesis; renal and kidney diseases such as transplant allograft rejection and fibrosis of the liver and kidney; bone remodeling diseases including osteoporosis; metabolic diseases such as atherosclerosis; and vascular diseases.
Compounds can therefore be directly targeting one or more kinases to achieve a therapeutic effect. Desirable targets of an inhibitor molecule are described below.
PDGF Receptor Family (Class III PTK Receptor Family)
Platelet-derived growth factor (PDGF) is a major mitogen for cells of mesenchymal origin such as fibroblasts, smooth muscle cells, and glial cells. PDGF is a 32 kDa protein heterodimer usually composed of two polypeptide chains, A and B, linked by disulfide bonds. In addition to the PDGF AB heterodimer, two homodimeric forms of PDGF exist, (AA and BB). During blood clotting and platelet adhesion, the PDGF is released from granules at sites of injured blood vessels, suggesting that PDGF may have a role in the repair of blood vessels. PDGF may stimulate migration of arterial smooth muscle cells from the medial to the intimal layer of the artery where the muscle cells may proliferate. The cellular proliferation induced by all isoforms of PDGF is mediated by ligand binding to the PDGF receptor. The PDGF receptor belongs to the class III tyrosine kinase family and consists of two receptor subtypes, termed type A (or type alpha), and type B (or type beta. Other members of the PDGF receptor family include CSF-1R, cKIT and FLT3.
FMS (CSF-1R)
CSF-1 is a potent growth and differentiation factor for bone marrow progenitor cells in particular those of the mononuclear phagocyte lineage. CSF-1 stimulates the proliferation and end-cell function of mature macrophages via specific receptors on responding cells. The biological activities of CSF-1 are mediated by a receptor of 165 kDa. The CSF-1 receptor is encoded by the c-fms gene which encodes the proto-oncogene c-FMS. As a member of the type III receptor tyrosine kinase family, CSF-1R has overall structural similarity to c-KIT, PDGFRα, PDGFRβ and FLT3. The receptor is a transmembrane protein with an extracellular ligand-binding domain of 512 amino acids, an intramembrane domain of 25 amino acids, and a cytoplasmic domain of 435 amino acids encoding a bipartite tyrosine kinase interrupted by a so-called kinase insert. Binding of the ligand activates the tyrosine kinase activity of the receptor. The cellular c-FMS proto-oncogene is the cellular homologue of a viral oncogene called v-FMS which is encoded by SM-FeSV (Susan McDonough strain of Feline sarcoma virus). The viral oncogene encodes a protein with a constitutive kinase activity.
Mutations activating the CSF-1 receptors have been observed in approximately 10 percent of the patients with myelodysplastic syndromes. A deletion of both alleles of the CSF-1R locus, which maps to human chromosome 5q33.2-3 in the vicinity of the receptor gene for PDGF, is found in the bone marrow cells of some of these patients (known as 5q minus syndrome). Mice with a targeted disruption of the c-fms gene are essentially a phenocopy of the op/op mouse, indicating that all of the actions of CSF-1 are mediated by the CSF-1R. These data indicate that a specific inhibitor of the CSF-1R would be expected to reduce monocyte production and macrophage numbers in vivo.
The major source of circulating CSF-1 is thought to be endothelial cells that line blood vessels, but a range of other cell types including fibroblasts, osteoblasts, monocytes, B cells, T cells and bone marrow stromal cells also produce CSF-1. Plasma CSF-1 levels are dramatically increased upon challenge with lipopolysaccharide or with infectious agents such as Listeria monocytogenes and Candida albicans. In humans, CSF-1 levels appear to be enhanced in patients with sepsis and LPS administration to cancer patients increased CSF-1 levels.
The involvement of macrophages in chronic inflammatory diseases such as rheumatoid arthritis (RA) is well established. In a murine model of collagen-induced arthritis, administration of CSF-1 exacerbated disease severity whilst an anti-CSF-1 antibody reduced the severity of established arthritis. CSF-1 has also been implicated as a contributor to disease severity in other arthritic models. Evidence exists for CSF-1 involvement in RA itself; synovial fibroblasts from RA patients produce CSF-1; CSF-1 levels were elevated in RA patient sera and synovial fluid.
There is an extensive literature on the contribution of CSF-1 to kidney disease.
Macrophage accumulation is a predictor of renal outcome in glomerulonephritis and correlates with kidney dysfunction in humans and elevated levels of renal CSF-1 are apparent in glomerulonephritis patients. In experimental disease models, there is clear evidence for the involvement of CSF-1 in directing excessive macrophage proliferation and tissue damage. The severity of lupus nephritis in MRL-1pr mice correlated with CSF-1 levels, whereas treatment with anti-CSF-1R antibody reduced local macrophage proliferation during experimentally-induced renal inflammation.
Multiple Sclerosis (MS) is a heterogenous disease in which various cellular infiltrates occur at different stages of the disease. In early steps, the immunopathology involves specific antigen recognition by autoreactive T cells and autoantibodies. In later stage, activated macrophages and glial cells predominate producing a large number of inflammatory mediators.
Alzheimer's disease (AD) constitutes a chronic cerebral inflammatory state that eventuates in neuronal injury. Microglia cells contribute to the pathophysiology of AD. CSF-1, a microglial activator is found at high levels in the central nervous system and augments β-amyloid peptide-induced microglial production of IL-1, Il-6 and nitric oxide which in turn intensify the cerebral inflammatory state by activating astrocytes and other microglia and directly induce neuronal injuries.
Expression of CSF-1 and its cognate receptor, c-fms have been detected at both the transcript and protein levels in Hodgkin's disease-derived cell lines derived from patients with nodular sclerosis. Inhibition of cell growth with antiserum to CSF-1 is indicative of an autocrine growth regulation pathway in these cells.
CSF-1 is produced by a very wide diversity of tumour cells in mouse and human and CSF-1 contributes to the attraction of large numbers of macrophages that are a significant component of the stroma of all solid tumours. CSF-1 is produced in more than 70% of breast tumours and may contribute to the overall disease through autocrine stimulation of the tumour cells, as well as through tumour-associated immunosuppression.
Macrophages attracted to the tumour by CSF-1 may also play a role in the metastatic spread of the tumour, and it has been shown that anti-CSF-1 therapy can diminish growth of human tumour xenografts in mice. Interestingly, ectopic expression of the native CSF-1R appears to be sufficient to generate transformation of non-malignant cells to clonogenic growth in vitro. In cells that are already clonogenic, CSF-1R expression can increase both clonogenicity and the size of individual clonal colonies formed in semi-solid medium.
There have been a number of reports indicating the CSF-1 can be expressed outside of the macrophage lineage, in testis, uterus, ovary and mammary glands, at some stages of development. A role for CSF-1 in normal development of the mammary gland in mice has been demonstrated, although this could be attributable to the crucial role of infiltrating macrophages in branching morphogenesis. By contrast, CSF-1R is expressed on a wide range of human solid tumours, notably breast, ovarian, endometrial and prostate tumours and also of B lymphocyte malignancies. A functional autocrine loop in these tumour types has been demonstrated based upon immunocytochemical localisation using antibodies directed against phosphotyrosine moieties on the active receptor, and the expression of a CSF-1/CSF-1R autocrine loop in breast and ovarian cancer is strongly correlated with disease progression and poor prognosis and is most likely causally linked to activation of the ras-raf-MAPK-Ets pathway inducing the production of invasive mediators, such as urokinase plasminogen activator. The most direct evidence for a causal role of CSF-1/CSF-1 autocrine/paracrine signalling in the progression stage of breast cancer came from crossing a mammary cancer prone mouse strain to the CSF-1-deficient op/op mouse strain, Lin and co-workers showed that cancer incidence was unaffected, but progression and metastasis were constrained in the absence of the growth factor.
It is well established that the skeleton is the most common site of distant metastases of breast, prostate, and lung carcinoma. The bone appears to provide a ‘fertile soil’ or environment for the cancer cells to germinate. Once tumour has metastasized to the bone, the disease is incurable due to bone pain, fracture, hypercalcemia and nerve compression. The bone is a repository of a number of growth factors and histology sections confirm that the tumour cells reside adjacent to osteoclasts and bone destruction in cancer is mediated by osteoclasts. Osteoclasts arise from a common progenitor as blood-borne monocytes and the activities of bone resorption is dependent on the actions of CSF-1, the ligand for fms and also RANKL. It has been demonstrated that many tumours spontaneously secrete large quantity of CSF-1 and RANKL is expressed by osetoblasts in the bone. In this respect, osteoclasts is reliant on CSF-1 and RANKL for their degradative activities.
The osteoclast, the exclusive bone resorptive cell, is a member of the monocyte/macrophage family that arises in vitro from myeloid precursors, with bone marrow macrophages representing the largest reservoir. Whilst M-CSF mediates the survival and proliferation of precursors of the monocyte/macrophage lineage and their differentiation into mature phagocytes supports the notion that cells of the myeloid lineage are osteoclast precursors suggested that M-CSF plays an important role in osteoclast biology and indeed, op/op mice, which fail to express functional M-CSF, are osteopetrotic.
Furthermore, administration of soluble M-CSF to op/op mice rescues their osteoperosis. The critical role played by the CSF-1/FMS axis in osteoclast differentiation suggests that manipulation of this axis by the use of a FMS inhibitor may be useful pharmacologically in situations where osteoclast function might be too high.
M-CSF has been implicated as playing a role in several diseases including inflammation. Most notable is the role of M-CSF in cancer, particularly angiogenism. Therefore down regulating M-CSF is an area of intense interest.
Atherosclerosis is a complex pathological process resulting from the interaction of inflammatory and fibro-proliferative responses. Administration of a macrophage-colony stimulating factor (M-CSF) monoclonal antibody (AFS98) to adult apolipoprotein E (apoE)-deficient mice demonstrated that the macrophage and M-CSF/c-FMS axis play an essential role in the arterial wall during development of the fatty streak lesion and that blockade of the M-CSF/c-fms pathway could act as protection from at least early atherogenesis.
Macrophages are a major component of the innate immune system. Their destructive potential is essential for protection against a wide diversity of infection, and is required for normal tissue turnover, remodelling during development and repair of injury. However, uncontrolled macrophage infiltration into tissues, or activated release of their products, causes much of the pathology of infectious, inflammatory and malignant disease. Therapies that control macrophage production, recruitment or activation are likely to have wide application in clinical and veterinary medicine. Osteoarthritis, in particular has been shown to be caused in part the over-production of macrophages in the synovial fluid of joints, leading to cartilage loss, inflammation and pain. One effective approach to the control of macrophage populations would be the generation of inhibitors of the CSF-1R, such as those described in this application. This would be desirable in diseases such as immunological and inflammatory diseases; hyperproliferative diseases including cancer and diseases involving neo-angiogenesis; renal and kidney diseases; bone remodeling diseases; metabolic diseases; and vascular diseases. Particularly therapies for myelodisplastic syndromes, rheumatoid arthritis, multiple sclerosis, Alzheimer's disease, Hodgkin's disease, kidney disease, human solid tumors including breast, ovarian, endometrial and prostrate tumors, osteoperosis and artherosclerosis.
PDGFRβ
The two PDGF receptor isoforms may be distinguished by their markedly different ligand binding specificities. PDGF beta receptor binds only B-chain (isoforms BB and AB), while PDGF alpha receptor can bind all forms of PDGF (isoforms containing A and/or B chain).
With the importance of PDGF-related processes to proliferation of endothelial cells and vascular smooth muscle, there are a range of pathogenic processes that an inhibitor of the PDGFRβ kinase domain could be used for diseases such as immunological and inflammatory diseases; hyperproliferative diseases including cancer and diseases involving neo-angiogenesis; renal and kidney diseases; bone remodeling diseases; metabolic diseases; and vascular diseases. Specifically, these include: restenosis, including coronary restenosis after angioplasty, atherectomy, or other invasive methods of plaque removal, and renal or peripheral artery restenosis after the same procedures; vascular proliferative phenomena and fibrosis associated with other forms of acute injury such as: pulmonary fibrosis associated with adult respiratory distress syndrome, renal fibrosis associated with nephritis, coronary stenosis associated with Kawasake's disease and vascular narrowings associated with other arteritides such as Takayasha's disease; prevention of narrowings in vein grafts; prevention of narrowings due to accelerated smooth muscle cell migration and proliferation in transplanted organs; other fibrotic processes, such as scleroderma and myofibrosis and inhibition of tumor cell proliferation that is mediated by PDGF.
KIT
Stem cell factor (SCF), also known as Kit ligand (KL), steel factor or mast cell growth factor is the ligand of the c-kit proto-oncogene product. W and S1 mice are two strains of mice with similar phenotypic defects in pigmentation. Both are anemic and sterile and have mutations in the c-kit and scf loci, respectively. SCF was first described as a pluripotent growth factor involved in the early stages of haematopoiesis, as well as in the development and function of germ cells and melanocytes. In addition, SCF may be implicated in inflammatory processes. More than thirty activating mutations of the Kit protein have been associated with highly malignant tumors in humans. The c-kit proto-oncogene is a Class III RTK, believed to be important in embryogenesis, melanogenesis, and hematopoiesis. There is evidence that this receptor is involved in the pathogenesis of Mastocytosis/Mast Cell Leukemia, Gastrointestinal Stromal Tumors (GIST), small cell lung carcinoma (SCLC), sinonasal natural killer/T-cell lymphoma, testicular cancer (seminoma), thyroid carcinoma, malignant melanoma, ovarian carcinoma, adenoid cystic carcinoma, acute myelogenous leukemia (AML), breast carcinoma, pediatric T-cell acute lymphoblastic leukemia, angiosarcoma, anaplastic large cell lymphoma, endometrial carcinoma, and prostate carcinoma. Accordingly, it would be desirable to develop compounds that are inhibitors of the tyrosine kinase activity of c-KIT receptor for use in diseases such as immunological and inflammatory diseases; hyperproliferative diseases including cancer and diseases involving neo-angiogenesis; renal and kidney diseases; bone remodeling diseases; metabolic diseases; and vascular diseases, such as the examples described above.
FLT3
FMS-related tyrosine kinase 3 (FLT3) is a receptor tyrosine kinase preferentially expressed in hematopoietic progenitor cells. Its ligand, FLT3-L, stimulates the growth of hematopoietic progenitors from the bone marrow, peripheral blood, and cord blood. FLT3-L appears to work in synergy with other hematopoietic growth factors exerting pleiotropic effects on precursors of both the myeloid and lymphoid lineages. In combination with myeloid growth factors such as granulocyte-macrophage and granulocyte colony-stimulating factor (GM-CSF and G-CSF), or CSF-1, FLT3-L increases the number of myeloid colonies generated from the committed colony-forming units. Similarly, there is evidence that FLT3-L synergizes with the interleukins IL-7, IL-3, and IL-11 to stimulate B lymphopoiesis in vitro, with IL-12 in the presence of thymic stroma to promote T cell development, and with IL-15 to drive the development of NK cells. Taken together, these observations suggest that FLT3-L is able to nuance the induction of the development of several hematopoietic lineages, by enhancing and/or modifying the action of other cytokines or interleukins.
Recent studies have indicated that the FLT3 gene is mutated by internal tandem duplication in 20-25% of adults with acute myelogenous leukemia (AML), leading to phosphorylation and overactivation of FLT3 activity in cancerous cells. AML is the most common type of leukemia in adults, with an estimated 10,000 new cases annually. FLT3 has also been implicated in neural-crest derived tumors and myelodysplastic syndromes. Furthermore, mutation of FLT3 at aspartic acid 835 (asp835) has been implicated in progression of AML. It is conceivable also that activation of the FLT3 receptor kinase leading to AML may occur in the absence of genetic mutations of the FLT3 gene. Inhibitors of FLT3 are presently being studied as potential AML therapeutics. For example, agonist antibodies that bind the extracellular domain of FLT3 and activate its tyrosine kinase activity have been described. More recent results indicate that FLT3 inhibitors have anti-tumor activity in pre-clinical models.
Accordingly, new and improved reagents for the detection of FLT3 activity would be desirable, including development of reagents against newly-identified sites of FLT3 phosphorylation. Since phosphorylation-dependent over-activation of FLT3 is associated with diseases such as AML, reagents enabling the specific detection of FLT3 activation would be useful tools for research and clinical applications.
Furthermore FLT3 inhibitors are likely to be useful in hyperproliferative diseases including myeloproliferative diseases such as AML.
VEGF Receptor Family
The Vascular Endothelial Growth Factor (VEGF) is a dimeric protein also known as vascular permeability factor because it acts on endothelial cells to regulate the permeability of those cells as well as their proliferation. These two activities are mediated through its tyrosine kinase receptors (FLT1, FLT4 and KDR), which are also regulators of angiogenesis. The KDR receptor mediates the biological activity of mitogenesis and proliferation of endothelial cells.
Angiogenesis is limited in normal adults primarily to wound healing, pregnancy and corpus luteum formation, but it is induced in many diseases including cancer (particularly pulmonary adenocarcinoma and non small cell carcinoma), diabetic retinopathy, rheumatoid arthritis, psoriasis, atherosclerosis and restenosis. Solid tumours particularly rely on angiogenesis for their growth, and successful metastasis also requires the presence of blood vessels to allow tumour cells to enter the circulation. Inhibitors of KDR will be useful in the treatment of diseases such as immunological and inflammatory diseases; hyperproliferative diseases including cancer and diseases involving neo-angiogenesis; renal and kidney diseases; bone remodeling diseases; metabolic diseases; and vascular diseases, including those described above.
SRC Family
The SRC and BTK families of kinases are important for normal cellular proliferation, however their over expression and over activation can promote the development of cancer. There are nine members of the SRC family of PTKs, including c-SRC, YES, FGR, FYN, LYN, LCK, HCK, BLK and YRK. The BRK family includes BRK, FRK (PTK5), SAD and SRM.
c-SRC is found in a broad range of tissues with especially high levels of expression in neuronal and heatopoietic cells. c-SRC is involved in cellular adhesion, invasion and motility of tumour cells.
The effects of elevated SRC kinase activity have been extensively studied in vitro using a variety of human neoplastic cell lines and in vivo with murine models. Using these systems, the effects of SRC on tumour initiation and progression were studied and suggested a role for c-SRC in almost every aspect of a cell's life including mitogenesis, proliferation, survival, control of cellular adhesion and migration, all of these processes are de-regulated during cancer progression. These factors led to investigation of a possible role of SRC in human tumorigenesis. Elevated SRC kinase activity has been found in human mammary carcinoma. Using a human breast cancer cell line, MDA-MB-231, which was injected into the left ventricle of Balb/C-nu/nu mice, a c-SRC inhibitor was seen to reduce morbidity and lethality, and also the incidence of metastases both in bone and visceral organs. The compound also inhibited osteoclast formation and bone resorption suggesting a direct inhibition of osteoclast activity and contribute to the reduced incidence of osteolytic lesions. One advantage for using SRC inhibitors for cancer therapy is that deficiency of SRC in mice appears to affect only bone cell formation with no effects on other organs.
In addition to breast cancer, elevated SRC activity has been reported in many other epithelial tumours including pancreatic, lung, ovarian, esophageal, colonic, neuroblastoma, melanoma, mesothelioma and gastric cancer. Cell lines derived from these tumours display up to 30× elevation of SRC activity.
In regard to the mode of SRC activation, SRC can be activated by receptor tyrosine kinases such as EGFR and HGF all of which are known to be active in the course of cancer progression. In this respect, SRC association with these receptor tyrosine kinases is instrumental in malignant transformation. C-SRC has also been implicated to interact with the JM domain of CSF1-R, a receptor tyrosine kinase that mediates CSF-1 signalling. CSF-1 is a key cytokine for growth and survival of cells of the mononuclear-phagocytic lineage and cells of this lineage have been known to associate with solid tumours and are known as tumour-associated macrophages (TAMs) that elaborate release of VEGF, MMPs and uPA, mediators that facilitate tumour metastatic processes. Furthermore, elevated epithelial co-expression of CSF-1 and fms has been shown in >50% of mammary tumours and autocrine CSF1-R activation has been shown to promote SRC-dependent disruption of junctional integrity in acinar structures in human mammary epithelial cells, a pre-requisite to tumour escape from primary sites.
A SRC inhibitor, AP23846, has been shown to reduce VEGF and IL-8 expression in human solid tumour cell lines and fails to support angiogenesis into gel foams implanted s.c. in mice. IL-8 is a pro-angiogenic factor that is a prognostic marker for many tumours and VEGF is an essential factor in support of angiogenesis. Other experiments have also shown that following VEGF stimulation, SRC preferentially associates with KDR/VEGFR-2 rather than Flt-1, the two main VEGF receptors present on vascular endothelial cells, thus highlight the potential significance of upregulated KDR-associated SRC activity in the process of angiogenesis.
The SRC family of kinases have also been implicated in bone remodelling diseases. For example, mice deficient in SRC develop osteoporosis because of depressed bone resorption by osteoclasts, suggesting that osteoporosis resulting from abnormally high bone resorption can be treated by inhibiting SRC. SRC inhibition may prevent joint destruction that is characteristic in patients suffering from rheumatoid arthritis. SRC is also required for replication of the hepatitis B virus, suggesting a role for SRC inhibitors in viral diseases.
Thus inhibitors of SRC family kinases could be useful for treatment of diseases such as immunological and inflammatory diseases; hyperproliferative diseases including cancer and diseases involving neo-angiogenesis; renal and kidney diseases; bone remodeling diseases; metabolic diseases; and vascular diseases. Examples include breast, pancreatic, lung, ovarian, esophageal, colonic, neuroblastoma, melanoma, mesothelioma and gastric cancer, pulmonary adenocarcinoma and non small cell carcinoma, osteoporosis, and rheumatoid arthritis.
EPH Family
The Eph family of receptor tyrosine kinases are epithelial cell kinases and family members include EPHA2, EPHA3, and EPHA8.
EPHA2 is a 130 kDa member of the EPH family. The function of EPHA2 has been suggested to include regulation of proliferation, differentiation, and barrier function of colonic epithelium, vascular network assembly, endothelial migration, capillary morphogenesis and angiogenesis, nervous system segmentation and axon path finding.
The ligand of EPHA2 is Ephrin A 1 and this interaction is thought to help anchor cells on the surface of an organ, as well as down regulating epithelial and/or endothelial proliferation. It is understood that under normal conditions the interaction helps regulate over proliferation and growth of epithelial cells, however if this barrier is prevented from forming or shed, prevention of proper healing may result.
As a result inhibitors of the EPH family of kinases, and in particular EPHA2 will be useful in a range of immunological and inflammatory disorders including interstitial cystitis (IC) and inflammatory bowl disease (IBD).
RET
RET encodes a receptor tyrosine kinase. Somatic chromosomal rearrangements involving the RET gene represent the most frequent genetic alteration in papillary thyroid cancer (PTC), the most common thyroid malignancy. As activating mutations of genes coding for tyrosine kinases occur early in cancer development, targeting these kinases provides a promising therapeutic opportunity.
Consequentially an inhibitor of RET is desirable for the treatment of a range of diseases including hyperproliferative diseases such as thyroid cancer.
There is therefore a need to develop inhibitors of one or more of FMS (CSF-1R), c-KIT, PDGFRβ, FLT3, KDR, SRC, EphA2, EphA3, EphA8, FLT1, FLT4, HCK, LCK, PTK5 (FRK) and RET, for therapies of a range of disease states including immunological and inflammatory diseases; hyperproliferative diseases including cancer and diseases involving neo-angiogenesis; renal and kidney diseases; bone remodeling diseases; metabolic diseases; and vascular diseases.